The invention relates to computers with a plurality of plug-in modules which can transmit or interrupt the transmission of interrupt signals from one module to the next.
Known computers of this type conduct an interrupt signal over a bus which is galvanically connected to each of a plurality of modules. Interrupt signals are sent over the bus and each module detects whether or not the signal is intended for it. To accomplish this each module has a decoding circuit which allows that module to ascertain whether the corresponding interrupt signal is intended for it and, upon receipt of the signal, to perform the appropriate operation.
To enable each of the remaining modules to process interrupt signals specifically intended for it, each module must relay signals not intended for it as rapidly as possible. This is best done within an especially narrow time frame when real-time processing is desired, because a worst-case-analysis must then be performed. In the most extreme case the interrupt signal must be conducted through every module, which for example, could involve addressing as many as 20 plug-in modules.
On the other hand, it is known to direct an interrupt signal simultaneously to all modules so that the intended module can accept the interrupt signal and generate an appropriate acknowledgement. It is, however, frequently desired to prioritize the signal on the basis of location. In such a case it is no longer possible to simultaneously direct the signal to all galvanically coupled modules.
A special problem arises when the modules are frequently changed to make use of the plug-in feature for adapting computers to desired system configurations. Such frequent module changes, though common in conjunction with computers that operate independently of their plug-in location, are not generally used with computers that employ plug-in locations having different addresses and capable of location prioritization. For remote modules, steps would be required to avoid an interference with the interrupt processing.
In many cases these would be complicated and nullify the advantages attained with the plug-in feature of the modules. Conceivable alternatives might be to short circuit the corresponding interrupt signal intended for a module that is missing, by employing a solder bridge, a jumper or a micro-switch that is responsive to the presence or absence of a given module, or the like. Even these alternatives are difficult to operate, are often forgotten and necessitate structural changes at considerable costs, as, for example, from additional protective shielding that may be required.